Molding, decorating and finishing die dried fibrous articles



May 31, 1966 J. c. WILLIAMS 3,253,970

MOLDING, DECORATING AND FINISHING DIE DRIED FIBROUS ARTICLES Filed Jan. 31, 1962 THIN, WET PREFORM D|E- DRIED PREFORM COMPOSITE DIE-DRIED ARTICLE IN VENTOH JOHN C. WILLIAM 5.,

United States Patent ()fiice 3,253,970 Patented May 31, 1966 3,253,970 MOLDING, DECORATING AND FINISHING DIE DRIED FIBROUS ARTICLES John C. Williams, St. Charles, 11]., assignor to Hawley Products Company, St. Charles, 11]., a corporation of Delaware Filed Jan. 31, 1962, Ser. No. 170,260 10 Claims. (Cl. 156228) Contoured preforms are made in the pulp molding industry by accreting fibers on a formed screen from a dilute fiber slurry. The preforms so produced may be oven dried directly as is done in the manufacture of egg cartons, or, to increase strength and definition, they may be pressed and dried in heated dies. These drying dies are foraminous, i.e. one die, usually the female is smooth, while the other die is perforated or drained. The drainage allows the steam generated in drying to escape. die drying apparatus of thistype is described in US Patent 1,983,553.

Housings and carrying cases have been made in great numbers using the die dry process. The preforms are made from a slurry of strong fibers, e.g. kraft, glass and nylon. They are from 200 to 400 thousandths of an inch thick as wet formed, and in the course of die drying are compressed down to 60 to 100 thousandths. It is customary to varnish dip and oven cure the dried preform for further strength and water resistance.

A die dried carrying case is rugged. It has a high strength/weight ratio. Impact resistance is particularly good. As it comes from the drying die, however, the finish is poor. This makes it difficult for the pulp molding industry to compete with plastics products which receive a high finish from the die in which they are molded. It is important, therefore, that there should be a method available whereby the pulp molded die dry article will come from the drying die With an acceptable finish, or at least in such condition that it can be finished with one coat of paint.

Many experiments have been carried out in an endeavor to improve the finish. There are, however, a number of formidable difiiculties in the process which must be surmounted. A partial list of these follows:

(1) Die drying is a pressing operation in contour. The wet preformed fiber mat will tear, but it will not flow. While a greatdeal of skill has been developed in the industry in fitting preforms to the drying die, even with the best possible fit, pressures can vary widely from the top of the piece (press pressure) to the side (wedge pressure).

(2) The contact of a wet preform against a 400 F. die surface gives an explosive evolution of steam which disrupts the surface fibers and makes them prone to fuzz up on painting.

(3) The fiber furnish employed must be free (rapid draining) and contain coarse fiber so that the heavy mats required can be accreted or felted. This free and rough character is necessary for the passage of steam during drying. It again makes for porosity in the finished piece, with difficult painting.

(4) Since one side of the die is perforated, there is a limitation on he amount and type of resin that may be added to the stock in the beater. A good molding resin which could give a surface finish might also plug the drainage system within a very few pieces.

(5) The compression of the pulp mat from around 300 thousandths to 80 thousandths of an inch on a straight side (in line with press travel) means that the descending die tends to tear the preform. Even a preform that is not grossly torn will have small cracks in it which are most difficult to finish.

In dies that close to make a uniform fixed aperture,

drying pressures depend on the weight of preform taken. Thus, in a housing shape, with flat top and straight side walls, light preforms are not pressed at all. As the preform weight increases into the proper range, the preform is pressed uniformly on the top and on the sides. Top pressure is press pressure. Side pressure, however, is developed during the descent of the female die and is wedge pressure. If the preform weight is increased farther, the descending die makes visible tears in the side walls, and at a high enough weight, the sides of the preform will be completely sheared off. The amount of side pressure that can be exerted thus depends on the resistance of the preform to tearing, i.e., green strength or initial wet strength. It is also governed by the design of the dies. A radius is put on the leading edge of the die to assist in ironing" the pulp.

Green strength of the preform is determined by the fibers selected, by the opening or beating used and by the amount of water in the preform. If the preform is made drier more side pressure can be applied in the die dry. Here are some illustrative figures for typical stock. The usual preform from the felting tank is 25% solids and will take 20 p.s.i. side pressure without tearing. It may be dewatered on the felter by applying a thin rubber blanket while the vaccum is still on. This brings solids to 32% and a 60 p.s.i side pressure may be obtained. If the preform is transferred to a presqueezing die where p.s.i. can be exerted on it, solids can be brought to 45% and side pressure during die drying may be as high as p.s.i. without causing tearing. Presqueezing, therefore, allows more diflicult contours to be made and die drying to be carried out at higher pressure. The rough pulps are still necessary, however, and it has unfortunately turned out that the part die dried at 150 p.s.i. does not have a plastic type finish. It will not finish with one coat of paint.

The difiiculties of the process have brought forth interesting devices, none of which has yet proved practical. In one, the die dry male is a rubber bag capped with woven spring wire. ing the drying operation; the spring mat expands as required, yet maintains an open space for the passage of steam. This method made hard pressed, fine surfaced, pulp molding which could be finished satisfactorily. However, after about fifty pieces had been die dried, the springs were pressed even with the rubber surface and drainage was lost.

It has been proposed to spray the wet preform with resins which are moldable, or even to accrete on the preform, in a second felting operation, a top layer rich in resin. Such coatings show the usual tears; so that while much of the surface may be sized for painting, there is also a certain amount that is not. Surprisingly, the finishes obtained in this method are mediocre. On research into the cause of this it was found that the wet felt shrinks in the drying die and very rapidly. loses contact with the polished die surface. In a standard production stock, blanketed, this shrinkage of wall thickness was found to be of the order of 13% of the die aperture.

It has been proposed to remold the preform with a dry resin containing surfacing sheet. This is practically impossible in the contours that the pulp molding industry is called on to produce. It has been proposed to make thin dry resin impregnated pulp molded preforms for use in surfacing the contoured heavy fiber piece in a second molding operation. There is merit in this idea, but still some practical difiiculties in the way. It is customary in the industry to run sets of two or three drying dies. These are never exactly of the same dimensions; the dry preform which willfit one die will not fit another. There are also changes in;dimension on cooling, in the customary varnish dipping and baking, and on rehumidification.

The bag is inflated to 250 p.s.i. dur- For example, a varnish impregnated piece will often be split if the drying dies are closed on it again. Storage, impregnation and handling of thin dry preforms, also, would be a major undertaking.

It is an object of the present invention to provide a simple method whereby the die dried. preform will be readily paintable.

It is another object of the invention to produce an attractive molded type finish directly from the drying die.

It is a further object to provide a hard and scuff resistant surface. Other objects will appear hereinafter.

In accomplishing these objects in accordance with this invention, a fibrous preform is die dried to produce an article slightly shrunk with respect to the original die dimensions, the dies are opened, a thin wet fibrous preform corresponding in its dimensions substantially to the dimensions of the die drying die is applied to the die dried article, and the dies are reclosed. After further die drying, the dies are reopened and the resultant article having a good surface finish is removed. In many cases, it is desirable to include a resin in the thin preform and/ or in the initial die dried preform. In such event, the kind and amount of resin treatment should be such as to insure compatibility between the initial die dried preform and the thin wet preform. Thus, since it is customary to use a Water Wet thin preform, the surface of the initial die dried preform should be Water wettable to insure cohesion of the two preforms.

The drawing is a diagrammatic illustration of the process aforedescribed, i.e., the application of a thin, wet preform to a die dried preform and the formation of the composite, die dried article.

The production of radio speaker diaphragms in the pulp molding industry has brought to a high degree of perfection the formation and handling of thin Wet accreted fibrous preforms. These are picked up from the forming screen after it emerges from the dilute slurry, by a shaped perforated transfer. Vacuum and air pressure are used to pass the preform from the felter to the transfer. From the transfer, the thin preform is ordinarily put onto a shaped drying screen, and dried by pulling hot air through it. According to the present invention, however, the thin wet preform is applied to the freshly dried heavy fiber molding while it is still on the die dry male, on the first opening of the press. The press is then reclosed for a short period to dry and mold the thin wet felt and to attach it to the under felt. A transfer device is necessary in large shapes; but it can be dispensed with in small parts, with the thin Wet preform being applied to the thick dry preform by hand, and the drying dies reclosed.

Almost all the diificulties of the die dry process mentioned are surprisingly eliminated in this procedure:

(1) A thin felt can be made with much more precision than can a heavy felt. It does not have the corrugated or bark surface, for example. It is being applied to something that has also just been very precisely formed, i.e., the heavy preform has been formed against the female die and then has shrunk away from it a small uniform amount. The felter for the thin felt has been dimensioned to exactly the female drying die size. Even if the fit should not be perfect, the thin wet preform can accommodate itself to minor discrepancies.

(2) The thin Wet felt can readily be pressed or partially dried to increase its strength. Thus, one thin felter can serve three heavy fiber dies. One dry piece comes off each minute from the three dies. It takes however only 5 seconds to form the thin felt, and-there are 30 seconds at least in which air, hot or cold, may be pulled through it, either on the felter or in the transfer. This can bring the solids to 50% range.

(3) Application of a thin Wet felt to a dry heavy preform is quite different in terms of die drying than was the original application of the heavy felt to the die dry male. Moisture will immediately go into the heavy fiber by capillarity, drying and strengthening the thin cap felt. This and the heat of the dried heavy preform will often bring the preform to total solids or even total solids before the dies are closed. The dried preform gives a resilient support to the thin overfelt. Instead of tearing the overfelt in closing, the female die can press it into the remoistened die dried heavy fiber piece. This resilience indeed means that there is pressure available to fiow an incorporated resin out against the smooth finish of the female die after the dies are completely closed.

If the three drying dies are reasonably close together in dimension it may be desirable to have three engaged in drying, and one of higher finish and more exactly controlled temperature engaged in molding the finishing thin wet felt to the dried heavy fiber part. In this operation a molded edge may also be provided as follows: The dried part while off the drying die may he saw trimmed and a top felt applied which is longer than the trimmed part. The end of the top felt is then turned over the saw trimmed edge and tucked inside the piece. This may be retained inside with small spots of an adhesive, though adhesive will not usually be necessary because the assembly is immediately applied to the male of the high finish die which holds the turned edges in place.

The high finish die dry tools have a molding ring which fits exactly against the trimmed edge with its cap felt cover. The dies are closed and the drying and molding of the overfelt completed. The molding ring exactly fits the aperture between male and female die when the dies are closed. There can be several rings provided to be used with different saw trims to make articles of different heights.

The molding ring can also have a thin section extending A to /2 inch up the side of the male die to cover the drainage pattern and to give a smooth inside to the piece for that distance. v

(4) The porosity of heavy die dried fiber, which is over 50% voids in the ordinary piece, has heretofore been considered a disadvantage. It is helpful, however, in the method of the invention because vacuum can be easily applied through the dry piece to pull the thin wet preform from the transfer. There is also enough How to accommodatethe steam of drying.

(5) Most of the limitations of stock that have been mentioned do not apply to the thin wet overlay felt. Since it is not dried against a permanent drainage system it can carry any desired amount of fiowable resin. Since it dries almost as a film, without having to pass steam from another portion, it may be of tight or hydrated stocks. Well hydrated cellulose has a grease-proof char acter which here is an aid in painting.

The thin finishing preform will constitute from 2 to 50% of the final dry weight. It can be made from stocks from 6 to second (Williams) freeness. It can contain from zero to 150% resin by weight based on fiber weight to give the desired finish. It can also contain mold lubricants, colored fibers, colored pigments and incompletely dispersed coarse color for decorative effects. It can be applied at from 20% to 90% solids. It can be printed as desired or decorated with patterns before being applied. If desired the heavy fiber part or the thin Wet felt can be pattern printed or stippled with an adhesive. This term stipple is used advisedly, since a complete film of adhesive would seal drainage and prevent drying. Two finishing preforms can be applied simultaneously or in sequence and the finishing preform itself can be a double felt.

It will be recognized by those skilled in the art that the thin wet overlay preform can be of the same stock as the dried heavy fiber part and still have utility in covering the small tears produced in the original die drying operation. By inducing further pressure (heretofore unobtainable in the straight sided die dry part) it also makes resin from beater sizing the heavy fiber more effective.

preform covered with a thin rubber blanket.

Vacuum on one side and atmospheric pressure on the The finishing preform is compacted to 3 to 50 thousandths of an inch in the die dried operation.

The invention will be further illustrated but is not limited by the following examples in which the parts are by weight unless otherwise indicated.

Example 1.Transfer described Contoured pulp molded die dried backs for television cabinets were made in the usual process as follows: 50 lbs. of ground wood, 150 lbs. of northern kraft, 75 lbs. of refined rag and 50 lbs. of shredded wood were dispersed in 120 F. water in a breaker at 3% consistency. At the completion of the fiber preparation, 80 lbs. of cationic melamine colloid (American Cyanamid Parez 607) and 56 lbs. ,of 50% total solids polyvinyl acetate emulsion (Bakelite Corporation, Vinylite WC- 130) were added. The freeness of this stock was seconds (Williams Freeness Tester, 2.5 gram pad). This television back production stock was pumped to a storage tank where it was diluted to 1.5% consistency,'.and from the storage tank it was metered as needed to the preforming tank which was maintained at 0.7% consistency. This rough type of pulp is required in order to be able to form mats of the proper thickness that can be dried in heated dies without blisters forming.

The television cabinet back was 27 x 29 inches overall and of approximately 80 thousandths thickness throughout. The edges were flat, with a 13 x 19 inch flat portion centrally located which stood out 2 /2 inches. The 2 /2 inch high walls in this section were essentially vertical, i.e., in line with press travel and having only 3 taper. The drilled and screened preform or felting die had the contour as described, as did the male drying die.

The felting die was placed on a movable platform in the felting tank and connected through valves to air pressure and vacuum supply lines. T 0 make the preform, the die was immersed in the fiber slurry with vacuum applied. This pulled water through the screen and felted out (accreted) a fiber mat in the desired shape. The screen was then brought back to the surface and the wet The other resulted in a further expulsion of water. The preform as made weighed approximately 3600 grams. Blanketing brought this down to 2700 grams and also compacted and strengthened the preform.

The blanket was removed, the vacuum cut off and a pulse of compressed air was used to blow the wet preform off the felter. The preform was between 300 and 400 thousandths thick at this time. The operator placed it in position on the perforated male dryingdie and closed the smooth high finish female drying die on it. Both male and female dies were heated by gas burners toapproximately 450 F. and the perforated male was connected to vacuum to remove expressed water and steam. The drying time was three minutes. The press was opened and the die dried television back was released from the male die with a pulse of compressed air.

The dried part weighed approximately 900 grams. It was dipped in varnish and baked one hour at 300 F. to give it strength and water resistance. This brought the weight to 950 grams. The next operation was die punching which provided the desired ventilating holes in the back for the television set. After this the part was given a seal coat of polyvinyl acetate emulsion, dried and sanded; and following this, sprayed with a coat of multicolor lacquer.

Painting was the most difficult operation of the process, the most costly and resulted in the most complaints from the customer. This is due to the built-in limitations of the die drying process. The essentially straight sides of the center portion of the piece were torn, cracked or soft or all three. The closing of the dies and simultaneous compression of the wet pulp preform from approximately were lost.

6 300 thousandths to thousandths thickness made outright rejects in 5% of the parts, since the pulp preform was torn and stipped away from the male die. In 10% more, the part looked passable, but the paint had vanished here and there into incipient tears where the fibers had been moved apart. In all the pieces the straight walls were so poorly pressed and of such low density that it was very hard to keep paint at the surface even though a prime or seal coat was used. The multi-color lacquer in these areas was dull and the pattern and color contrast 30% of the parts needed retouch spraying.

If a heavier preform is used, e.g. one that will give a 1100 gram dry piece instead of 900, the wedge pressure developed on the straight walls can be very appreciable. However, this raises tear rejects from 5 to 50%, or, as weight is raised further, even to It also tends to stop the closing of the press, so that the flat surfaces are unpressed and become porous in turn.

The process as described in thus limited to about 60 psi. pressure in the die drying for straight sided pieces. This limitation is imposed by the strength of the blanketed pulp at approximately 33% total solids and its ability to resist being dragged off the die during closing of the tools. The difficulties were almost completely eliminated by the method of the disclosure which was used as follows. On the opening of the drying dies, while the dry television back was still on the perforated male (the usual pulse of blow oif air was omitted), an approximately 30 thousandths thick, closely fitting, wet preform was applied and the press closed again for 30 seconds, to dry and attach the thin preform to the part. The overlay felt molded down to approximately 10 thousandths of an inch thickness and. covered tears and incipient tears in a most satisfactory manner.

The advantages of applying a wet surfacing preform are manifold. It is possible to fit the light preform very closely to the dry felt. Light preforms of highly beaten stocks can be formed, dewatered, and dried in a reason able time, even though the stock freeness is in the 20 to 100 seconds range. They do not require rough fiber. In other words they can be designed exactly for the surfacing and finishing function. Highly beaten stocks even when dried without pressure tend to be greaseproof. This feature holds paint at the surface and makes finishing much easier.

The overlay felt has less tendency to tear than the original felt. This is partly because with stock as given the part shrinks away from the female mold in drying,

leaving room for the overlay. It is partly because drying into the hot piece is rapid and well established at the time the dies close again. It is also due to the fact that a (dewatered) beaten pulp is usually stronger than a raw pulp (at the same fiber solids). Should tearing be encountered, the felt may be made thinner, stronger stocks selected, time of beating varied etc. Finally, if tearing does occur, it does not mate with the small tears of the original piece, so there is no continuity of tear.

It was found that when 40 second freeness pulp, as described below, was applied and dried to the dry television back and the part varnish dipped, adhesion was satisfactory. Painting became so much easier that it was possible to dispense with the polyvinyl acetate seal coat.

The second thin felt was made from 20 lbs. bleached northern kraft, 20 lbs. refined rag and 10 lbs. ground wood brought to 40 seconds freeness in a beater, with 15 lbs. of 10% Parez 607 and 15 lbs. of Vinylite WC added. This stock was dispersed at 0.2% consistency in a sparate tank and felted in the usual manner in a 10 second felter immersion. The drilled felter form used had such dimensions that it would accurately fit into the female drying die. When the form was screened with 40 mesh wire of 20 thousandths inch thickness, enough en-' largement was obtained so that the wet thin preform made would fit on the dried part in the press.

'7 The thin felt was blanketed as usual. It was too weak to be taken off the screen and applied by hand. It was, therefore, picked up and applied by a transfer device.

A transfer as used here consists of a perforated shaped metal screen formed to fit the new felter with the 30 thousandths inch overlay preform as made on it. The

first screen is backed up by a heavier spinning, also perforated as required. These are fastened in a housing which has a hose connection and suitable valves so that vacuum can be applied and released, and a pulse of compressed air given if desired. The transfer is provided with hand grips and is registered against guide rods both in picking up and depositing the thin felt. In taking the felt, the transfer is pressed down hard on the felter, vacuum is cut ofi the felter and applied to the transfer. Meanwhile, the felter is opened to atmospheric pressure 1 or, a pulse of air is given to it and the operator lifts the transfer straight up, bringing the felt. The transfer and felt are then registered and pressed down on the male drying die. The vacuum is cut off the transfer and applied to the male die dry and the porous dry piece thereon. The transfer is meanwhile opened to air pressure, or given a pulse of compressed air and the preform is deposited. The transfer is then lifted away and the press reclosed.

While this is described as a manual operation, it is carried out in the same sequence in automatic machinery.

Example 2.Imprvement of a chair shape, using the same stock A chair of rather simple shape, i.e., a large cone which was subsequently mounted on tubular metal legs was being die dried in a fixed aperture die in automatic equipment. The automatic felter performed the following operations:

(1) The female felter descended into the 0.5% consistency pulp (television back production formula of Example 1).

(2) The felter pressed the Wet felt against a screened fitting form (the transfer) to assist in dewatering it.

(3) The vacuum was replaced in the felter with 2 p.s.i. air pressure, while vacuum was applied to the transfer. This caused the preform to stay with the transfer while the felter again descended into the slurry.

(4) The heated perforated female drying die was now brought against the wet preform in the transfer and passed to it by a similar manipulation of pressures.

(5) The die dry tools were closed for 3 minutes to complete drying.

(6) The dry part was blown by a pulse of air onto the male die as the dies opened and from there ejected by air onto a platform brought in to receive it.

The dried chair weighed from 2200 to 2500 grams. It was saw trimmed, varnish dipped and stoved.

This chair was strong and satisfactory in an upholstered model. However, it was not well enough molded, because of the inherent difliculties of the process, to market with a smooth painted finish.

Due to the easy contours of this particular chair, an unusual application of the invention could be made. It was found that a light (350 grams dry) preform would pass to the transfer from the original felter.

Step 6 was accordingly modifiedso that vacuum retained the preform on the female on opening the press. Die and part then traveled to the transfer and accepted the thin felt and returned. The dies were closed for 40 seconds to complete the drying. Ejection was then as in 6.

This second felt filled out the dies and made both a smoother and stronger molding. The part was trimmed, varnish dipped and given a pigmented latex spray coat. One coat gave an acceptable finish.

Example 3.Dental tray Trays for taking dental impressions are often made of stainless steel. They are expensive, hard'to clean and even painful to use because of poor fitting. It is obvious that a fibrous tray would be at a great advantage because of cheapness, disposability and ease of tailoring to the patients mouth. The edges can be scissor trimmed. There is also the esthetic consideration of having the one use article.

To be satisfactory, the fibrous tray must keep its shape while wet, yet not be so water repellent that the plaster will not stick to the casting surface. This was arranged by the technique of the invention. The casting surface (towards the teeth) was taken from the drained side of the drying die, e.g., from formed perforated metal. This roughness produced by the perforation in the die dry part was an aid in making the plaster stick. The first felt was made from 4540 grams of bleached kraft opened at 3% consistency with the water at 150 F. To this was added 1360 grams of 10% Parez 607 cationic melarnine wet strength resin and 900 grams of Vinylite WC- polyvinyl acetate emulsion. After 3 minutes mixing this batch was pumped and diluted to felting consistency of 0.8% with cold Water. It was then felted into dental tray preforms and die dried in the usual manner for 2 minutes to give a 50 thousandths inch (approximately) thick part. On the first opening of the mold, with the part still on the perforated male, a wet overlay felt of approximately 60 thousandths inch of the following stock was applied: 10 lbs. bleached kraft at 30 seconds freeness treated in the beater with 4 lbs. of caustic dissolved phenolic resin (Monsanto Chemical Company, Resinox #594) and the pH brought to 5 With phosphoric acid. Application was by transfer and the dies were closed for an additional 40 seconds. The part was blown olf by air pressure. It thus consisted of a shaped dental tray with a water wetting liner adapted to assist in the setting and adhering of the plaster, while the outer portion which contacts saliva was dimensionally stable and essentially waterproof, due to the phenolic resin. It will be observed that the method of the invention protects the drainage system of the mold from flow of the -resin.

Example 4.-Applicati0n of the method of the invention to improving forming boards A 24 x 30 inch tray with one inch deep contoured sides was being molded from Weyerhaeuser Pres-took, PT-lO. This material is produced by the Weyerhaeuser Company, New Products Division, Molded Products Department, Tacoma, Washington and is described by that company as a flat, moldable panel comprised of chemically clear whole wood fibers which are thoroughly blended with thermosetting and thermoplastic additives manufactured under one or more of the following U.S. Patents, 2,405,213; 2,757,114; 2,757,149; 2,757,150 and 2,759,837.

The low density mat was handled according to instructions as follows: The panel was inserted in a sealed compartment and the air quickly displaced with saturated steam at atmospheric pressure. After 10 seconds, the heated and humidified mat was removed, and the 350 F. die quickly closed at 500 p.s.i. for 40 seconds.

It was found that the corners of this piece at the sharp radii were poorly formed. Accordingly on the opening of the press at 40 seconds, with the part on the male, a 40 thousandths inch fitting wet preform of the resin containing the overlay stock of Example 3 was applied and dried in a second closing of 30 seconds duration. This covered the spots of poor molding and improved the finish and durability of the whole tray surface. The moisture here was removed by breathing the die at 10 and 20 seconds after applying the overlay felt.

Example 5.Aeceptable finish direct It was desired to produce a phonograph case which would come from the drying die with an acceptable finish. This was not considered a possibility until the method of the invention was available.

' of the resin solution.

- 9 The case was 12 x 15 inches with inch high side walls. The walls had at 5 taper. Wall thickness was 90-105 thousandths inch throughout the case. The preform was made from the production television back stock as given in Example 1. The wet preform was 350 to 400 thousandths inch thick. It was dried in a high finish, chrome plated drying die electrically heated to 380 F. The male-die was perforated and gas heated. Vacuum was applied to the male during the drying operation.

The press was opened with the dried part on the male die. It had the usual porous and unattractive surface. Small tears were visible on the sides. An approximate 40 thousandths inch thickness wet overlay preform was applied by a transfer procedure and dried, molded and attached in a second closing of the dies of 50 seconds duration. The male felter for-the thin felt had the dimensions of the high finish female die. When the press opened, the part was blown off the perforated drying die male with a pulse of compressed air. The surface of the cabinet was now glossy, Waterproof and attractively colored. Barcol hardness had risen from 30 to 60 (Barber-Coleman Co., Instrument GYZJ 936).

The overlay fiber Was made. as follows: 1000 grams of northern kraft, 500 grams refined rag, 200 grams ground wood, were opened in the 10 lb. beater at 150' F. and then cut until 'freeness was 35 seconds. 400 grams of water ground Mapico red was added and circulated (Mapico red #516 Dark, Columbian Carbon Co., Mapico Iron Oxides Unit, Trenton, New Jersey). 1% reaction product of tetraethylene pentamine and Epon 828 were now added, based on the fiber, followed by 4% Oroprene 100 (Chemfax, Inc., 3 Rivers Road, Gulfport, Miss.). 4% polystyrene (both from xylol solutions) and 25% Resinox #594 (a one step phenolic) from caustic solution. After these were mixed in, the pH was dropped to 5 with phosphoric acid. The batch was diluted to 0.5% consistency with cold Water and stirred until thoroughly dispersed. It was then supplied to a small tank kept at 0.2% consistency and made into the thin overlay felts as required.

The molded surface produced in this example, also could be finished satisfactorily with one coat of an emulsion paint, single or multicolor.

Decorative efiects were obtained also by spraying the wet overlay preform lightly with 30% Resinox #594 (diluted with alcohol) before application. This made the preform sticky and the transfer could not be used.

It was found advisable here to give the preform an oven treatment (10 minutes at 150 F.) to reduce the mobility Example 6 .Transfer as felter Example '5 was repeated using a simplification of the Example 7.Special felter In preparing 50 pct covers to house the back of a dynamic loud speaker the process of the invention was carried out with a minimum of retooling, as follows: The pot cover was 5 inches in diameter at the base, 4 inches in diameter at the top and 3% inches high. One pot cover was die dried in the old brass tools from a waterproof stock and drilled-approximately every quarter inch with a 7 inch drill. The waterproof stock was made as follows: 50 lbs. of northern kraft, 20 lbs. of ground wood and 30 lbs. of refined rag were beaten to 20 second freeness and brought to 150 F. This stock was treated with 1 lb. of a reaction product of tetraethylene pentarnine and Epon 823 described in my now abandoned application, Serial No. 129,516, filed August 7, 1961, i.e., a hydrophilic resin prepared by reacting the polyepoxide (Epon 828) and the tetraethylene pentamine at a temperature of 120 F. to 350 F. in the approximate proportion of two reactive amino groups per epoxy group to give a hydrophilic adduct, further reacting the resulting adduct with the same polyepoxide in proportions suflicient to produce a hydrophilic adduct containing free epoxy groups and to give a molar ratio of epoxy groups to reactive amino groups of'0.85:1 to 2.5 :l, and stopping the reaction short of gel formation, e.g., by adding hydrochloric acid. Then 4% Panarez 7-70 (Amoco Chemical Corp.) from a 70% solution in naphtha, 4% polystyrene molding grade 30% in xylol, and 7% Resinox #594 from a 5% solution in dilute caustic were added and the pH reduced to 5 with phosphoric acid. The usual 40 mesh screen was rolled around the part and a screen Example 8.Triple felt In improving a defroster nozzle use to spread heated air over the inside of an automobile windshield, it was considered important to make (a) a sound absorptive structure to contribute to silence in the car; (b) interior smoothness to promote air fiow and (c) low porosity. Naturally the strength and ruggedness of the usual product must be retained.

The nozzle fitted at the base to a 3 inch flexilble hose, and in a length of 8 inches fanned out to 15 inches wide and a inch slot. The two sides of the fan were made in one die drying operation; the piece was varnish dipped and stoved, then punched apart and the two parts glued together face to face in the nozzle shape. The drainage marks printed on the piece by the perforated side of the die were turned outward in this operation, leaving the interior reasonably smooth for air flow.

The weight of the piece from the drying die was from 92 to 105 grams. It was made from a coarse pulp in order to promote drying. Thus 200. lbs. northern kraft, 20 lbs. refined rag, lbs. shredded wood were opened by propeller action in a breaker tub. Freeness was 9 seconds.

In improving the product according to the method of the invention, the preform weight was dropped to grams and on the first opening of the press a wet (10 grams dry weight) felt of refined rag (freeness 10 seconds) was applied and dried in a second press closing of 30 seconds. This gave an improved surface to the part at the die dry, but it became rough and porous after the varnish dip.

Accordingly, a second thin wet felt was applied and dried in 20 seconds, making a total of three preforms. This felt was 5 grams dry and was made from bleached northern kraft beaten to 50 second freeness and carrying 3 pounds Parez 607 to pounds of dry pulp. This was satisfactorily smooth even after the varnish dip.

It will be noted that the screened bronze casting of the felter for the two cap felts was a snug fit to the smooth die of the drying molds. The two cap felts were close enough to the same size so that the same transfer could he used for both. It was simple mechanical matter to swing the oversize felter from the rag tank to the beaten white kraft tank.

The new product was unique in having the strength of the shredded wood and kraft in the first felt, the sound 5.1 absorptive layer of rag in the second and the smooth beaten bleached kraft surface to promote air flow.

Example 9.-Prdncti0n of luggage shells surfaced with textryl In the regular production of quality luggage shells, the composition (by weight) of 50% northern kraft, shredded wood, 25% refined rag and %1 /2 inch cut glass fiber roving was felted and dried into a contoured luggage shape. These were dipped in varnish, stoved, saw trimmed and covered (as far down as possible) by heat sealing a cloth backed embossed vinyl film to the surface. This process makes superior luggage. However the cloth backed vinyl sheet is expensive. It must be warehoused in quantity in a variety of colors for production; and it can only be stretched down the sides approximately two inches.

It was therefore found advantageous to use the method of the invention to apply a textryl overlayer to the die dry felt, molding it to shape and drying it in a second closing of the dies.

As stated in Du Pont Textile Fibers, Technical Service Section, Wilmington 98, Delaware, #NP-19, December 1960, page 7, The generic name of textryl has been given to sheet structures made on the paper machine from fibrids and man made fibers Fibrids are filmy or fibrous binder particles. The morphology gives them the self bonding features of natural wood pulp. Such fibrids develop excellent bonds to synthetic fibers when heat is applied. Also see US. Patent 2,988,782, Process for Producing Pibrids by Precipitation and Violent Agitation, by Parrish, McCartney and Morgan, assigned to Du Pont.

Following the directions of the Textile Fibers Bulletin, Dacron binder #201 was dispersed in water at 1% solids and then 3 denier inch, type 54, semi-dull Du Pont Dacron stirredin. The proportion used was fibrid binder to 75 of the 3 denier fiber by dry weight.

The basic luggage shell was made from the original stock, adding however, 10% phenolic resin and 5% rubber latex in the beater so as to avoid the necessity of varnish dipping. The luggage shell was 12 X 16 inches in area with side walls of 3 inches. The dry weight untrimmed was 400 grams.

The fibrid stock was felted into preforms from a felter which would just drop into the female die. When picked up by transfer they could be applied while wet to give an exact fit to the dried luggage part on the die dry male. The dies were then reclosed to give a molding and drying to the overlay felt. Silicone lubrication of the dies was necessary to avoid sticking in this molding.

To improve the appearance and properties of the textryl outer coating, the part was taken hot from the drying die and pressed (with a molding bag) at 700 psi. for seconds in an embossed female die at 400 F.

The textryl coating was formed over and to the bottom of the piece without a seam. ever; this was taken care of by decorative stitching. To obtain adhesion, the first felt was stippled after die drying with Daran polyvinylidene chloride latex 202 and the textryl preform applied. This adhesive treatment could also be given after the die dry and before the embossing step.

Following the Du Pont instructions the textryl overlay could be colored as desired in the process.

The invention is especially useful when the initial wet preform is 200 to 400 thousandths of an inch thick, is die dried to 60 to 150 thousandths of an inch thick, a thin wet preform from 20 to 100 thousandths of an inch is It was not adhered how- 12 added and the latter is compacted to 3 to 50 thousandths of an inch by die drying the composite article.

The invention is hereby claimed as follows:

1. A process of preparing a molded article which comprises die drying a wet fibrous preform to produce an article slightly shrunk with respect tothe original die dimensions, opening the dies, applying a thin wet fibrous preform to the die dried preform, and remolding and drying the latter assembly of said die dried preform with the thin, wet fibrous preform applied thereon in dies of the original dimensions. I

2. A process as claimed in claim 1 in which a plurality of thin wet fibrous preforms are applied to the die dried preform and remolded and dried successively in dies of the original dimensions.

3. A process as claimed in claim 1 in which said thin wet fibrous preform contains 20% to solids.

4. A process as claimed in claim 1 in which the thin preform constitutes from 2% to 50% of the final dry weight of the article.

5. A process as claimed in claim 1 in which the thin wet preform contains up to 150% resin by weight of the fibers in said preform.

6. A process as claimed in claim 1 in which an adhesive is stippled between the die dried initial preform and the thin preform prior to the second die drying operation.

7. A process as claimed in claim 1 wherein said die dried preform is water-wettable and is rewetted by capillary action when said thin, wet, fibrous preform is applied thereto, thereby improving the cohesion between the ried preforms.

8. A process as claimed in claim 1 wherein said fibers of said die-dried preform are selected from the group consisting of raw wood fibers, chemical kraft pulp fibers, mixtures of raw wood fibers and chemical kraft pulp fibers and mixtures of at least one member of the group consisting of wood fibers and chemical kraft fibers with at least one member of the group consisting of glass fibers and cloth fibers; and wherein the fibers of said wet preform are selected from the group consisting of chemical kraft pulp fibers, cloth fibers, synthetic polymer fibers, and mixtures of chemical kraft pulp fibers with at least one member from the group consisting of cloth fibers and raw wood fibers.

9. A process as claimed in claim 8 wherein said both of said wet preforms are water-wetted prior to respective 'die-dryings thereof, and the surface of said die-dried preform is wetted by the water of said thin wet fibrous preform when the latter is applied to the former.

10. A process of preparing a molded article which comprises die drying a wet fibrous preform which is initially 200 to 400 thousandths of an inch thick to compact said preform to 60 to 150 thousandths of an inch thick, applying a thin wet fibrous preform from 20 to thousandths of an inch thick to the die dried initial preform and compacting the thin wet preform to 3 to 50 thousandths of an inch thick by die drying the composite article composed of the die dried preform and the thin, wet fibrous preform applied thereon.

References Cited by the Examiner UNITED STATES PATENTS 2,319,267 5 1943 Sawyer 15 6224 2,558,166 6/1951 Barnes. 2,832,267 4/1958 Runckel 161-460 EARL M. BERGERT, Primary Examiner.

H. F. EPSTEIN, Assistant Examiner. 

1. A PROCESS OF PREPARING A MOLDED ARTICLE WHICH COMPRISES DIE DRYING A WET FIBROUS PREFORM TO PRODUCE AN ARTICLE SLIGHTLY SHRUNK WITH RESPECT TO THE ORIGINAL DIE DIMENSIONS, OPENING THE DIES, APPLYING A THIN WET FIBROUS PREFORM TO THE DIE DRIED PREFORM, AND REMOLDING AND DRYING 